Heat shrinkage,oriented laminated plastic film

ABSTRACT

A LAMINATED, TUBULAR, THERMOPLASTIC FILM HAVING EXCELLENT PACKAGING AND SHIPPING ABUSE CHARACTERISTICS PRODUCTED BY CONTINUOUSLY EXTRUDING A LAYER OF AN ETHYLENE VINYL ACETATE COPOLYMER ONTO A TUBULAR SUBSTRATE OF A PREDOMINANTLY ETHYLENE POLYMER MATERIAL AND CONTINUOUSLY EXTRUDING AN ADMIXED ISOTACTIC POLYPROPYLENE, POLYBUTENE-1 AND ATACTIC POLYPROPYLENE POLYMER LAYER AS THE OUTER LAYER THEREON AND THEN ORIENTING THE RESULTING LAMINATE.

Aug. 27, 1974 H. G. SCHIRMER HEAT SHRINKABLE, ORIENTED LAMINATED PLASTICFILM Original Filed March 23, 1970 4 Sheets-Sheet 1 FIG.

8- 27, 1974 H. G. SCHIRMER 3,832,270

HEAT SHRINKABLE, ORIENTED LAMINATED PLASTIC FILM Original Filed March23, 1970 4 Sheets-Sheet 2 [III/Ill 34 FIG. 4

fl- 27, 1974 I H. G. samuzn 3,832,270

HEAT SHRINKABLE, ORIENTED LAMINATED PLASTIC FILM Original Filed March23, 1970 4 Sheets-Sheet 3 FIG. 5

FIG. 6

8- 27, 1974 H. G. SHIRMER 3,832,270

HEAT SHRINKABLE, ORIENTED LAMINATED PLASTIC FILM Original Filed March23, 1970 4 Sheets-Sheet &

United States Patent Int. Cl. B32b 27 /30 U.S. Cl. 161-165 4 ClaimsAABSTRIACT OF THE DISCLOSURE A laminated, tubular, thermoplastic filmhaving excel lent packaging and shipping abuse characteristics producedby continuously extruding a 'layer of an ethylene vinyl acetatecopolymer onto a tubular substrate of a predominantly ethylene polymermaterial and continuously extruding an admixed isotactic polypropylene,polybutene-l and atactic polypropylene polymer layer as the outer layerthereon and then orienting the resulting laminate.

This is a division of application Ser. No. 21,793, filed Mar. 23, 1970,now U.S. Pat. 3,754,063, which is a continuation in part of my copendingapplications U.S. Ser. No. 659,940, filed Aug. 11, 1967 now U.S. Pat.3,607,505 and U.S. Ser. No. 768,955, filed Sept. 23, 1968 now U.S. Pat.3,808,304, which was a continuation of Ser. No. 355,522, filed Mar. 18,1964, now abandoned, all assigned to the same assignee as thisapplication.

This invention relates to extrusion=coated or laminated, oriented,heat-shrinkable films and the method for continuously producing them.

The use of heat-shrinkable thermoplastic films in many packagingapplications is well established. Usually a productis enclosed in afilm, sealed, and then heat is applied thus shrinking the film snuglyabout the product. One of the mostuseful and satisfactory thermoplasticmaterials for packaging film has proven to be polyethylene. A number ofmethods are available in the prior art to convert raw polyethylene intoa suitable, heat-shrinkable packaging film. One method is taught by U.S.Pat. No. 2,855,- 517 issued to W. C. Rainer et al. on Oct. 7, 1958.Another method is taught by U.S. Pat. No. 3,022,543 issued to W. G.Baird, Jr. et al. on Feb. 27, 1962. In the Baird method, polyethylene iscontinuously extruded in the form of a tube, drawn, irradiated withelectrons at a dosage between 2x10 and 20 10 REP, heated, and stretchedagain by applyinginternal pressure to the tubing. The resulting filmusually has good heat-shrinking properties but relatively low tearstrength. Once a tear has begun it tends to rapidly propagate during theheat shrinking process resulting in destruction of the film.

Therefore, it is an object of this invention to provide a heatshrinkable film with improved'packaging and shipping abusecharacteristics. This includes improved tear strength at roomtemperature as well as at shrinking temperature and greater burstingresistance when shrunk taut about a deformable product and subjected topommelling.

Another object is to provide a film which will shrink at relatively lowtemperatures.

Another object is to provide a laminated, tubular film which can readilybe made into pouches and bags.

Yet another object of the invention is to provide a heat shrinkablethermoplastic film having improved heat sealing properties.

Still another object is to provide a film having higher gloss andhardness.

A further object is to provide a film which is easier to handle, stack,and use when made into pouches and bags.

These and other objects are achieved by the present invention whichprovides a laminated thermoplastic film having an initially unorientedtubular thermoplastic substrate that is oriented subsequent to thelamination or coating. The substrate is laminated with an outer coatingof a polymer of a mixture of 3058% by weight of isotactic polypropylene,22-50% by Weight of polybutene-l, and 520% by weight of atacticpolypropylene, cooled, reheated, and oriented. The resulting laminatedfilm has considerably higher abuse characteristics than an oriented filmalone; and, in addition, retains high shrink tension and free shrinkingability.

The novel method for producing the laminated film comprises the steps ofproviding cross-linked and unoriented thermoplastic tubing, extruding athermoplastic coating of a polymer of a mixture of 30-58% by weight ofisotactic polypropylene, 2250% by weight of polybutene-l, and 5-20% byweight of atactic polypropylene onto the tubing without stretching ororienting same, cooling the resulting laminated tubing, reheating thelaminated tubing to the orientation temperature of the coating and thenstretch-orienting the composite tubing.

The preferred substrate is a predominantly polyethylene material and themost preferred material is a polyethylene copolymer with 24% vinylacetate. It is preferred that the substrate be irradiated prior tocoating. Preferrably the outer coating is secured to the substrate by arelatively thin coating or lamina of an adhesive polymer material thatcan be hot blown at the temperatures of orientation of both the outercoating or lamina and the inner substrate or lamina. The preferredadhesive lamina is a polyethylene copolymer with 8-13% vinyl acetate.

The invention may be better understood by reference to the followingdetailed description and drawings in which;

FIG. 1 is a schematic diagram of a preferred method for carrying out theinvention;

FIG. 2 is a cross-section of the die head used in the present invention;

FIG. 3 is a view taken along line 33 of FIG. 2;

FIG. 4 is a cross-sectional view of the laminated fil of the presentinvention; 9

FIG. 5 is a cross-sectional view of an improved bag made from thelaminated tubing showing the curlproduced at the bag open'ing;-

FIG. 6 is a schematic representation of the. bag of FIG. 3;

FIG. 7 is a graph showing a number of runs of said invention as setforth in Example II through XVI and the interpetation thereof based onthe inventors knowledge of the art and observations of the Exampleprocedures; and

FIGS. 8a-8c are graphic showings of preferred embodiments of the outercoating as interpreted from the results of the Examples and the graph ofFIG. 7 and the inventors projections thereof.

Referring to FIG. 1, a conventional extruder 9 is shown into which isfed ethylene vinyl acetate copolymer having 3 /2% vinyl acetate byweight. The tubing 10 is extruded downwardly from die head 11 which is.fed from extruder 9. After cooling by water spray from cooling ring 12the tubing is collapsed by pinch rollers 13 and is fed through anirradiation vault 14 surrounded by shielding 15 where it is irradiatedwith electrons from an iron core transformer accelerator 16. Otheraccelerators such as a Van der Graafi or resonating transformer may beused. The radiation is not limited to electrons from an acceleratorsince any ionizing radiation may be used. The unit of radiation employedherein is the rad which is defined as that amount of radiation whichwill dissipate 100 ergs of energy per gram of irradiated material byionizing particles. The mr. is one million (10 rad.

The time of irradiation of the polyethylene tubing 10 is not criticalbut need only be enough to give the required dosage to effectcross-linking. In the present embodiment the radiation dosage should bein the range of about 2 to 8 mr., but preferably 4 to 6 mr. In the priorart it is usually desirable to irradiate to about 12 mr. At the lowerdosages usable with the present invention the irradation efficiency perpound of tubing is greatly increased and sealability is increased.

The tubing 10 is guided through the irradiation vault 14 by rollers 17;and, after irradiation, the tubing 10 goes through pinch rollers 18following which it is slightly inflated by a trapped bubble 20 but notstretched longitudinally as the rollers 18 are driven at the same speedas rollers 13. The tubing is inflated only enough to provide asubstantially circular tubing without significant transverseorientation. The slightly inflated tubing 10 passes through vacuumchamber 21 and through a laminating die 22 where the thermoplasticcoating 23 is extruded onto the inflated tubing 10 thus forming laminate24. The die 22 is fed molten thermoplastic from a conventional extruder25. In the most preferred embodiment the coating is ethylene vinylacetate copolymer having 9 /2% vinyl acetate by weight. Ethylene vinylacetate copolymers having a vinyl acetate content in the range between7% and 13% by weight are preferred thermoplastic coatings with thosehaving a vinyl acetate content between 9 /2-10% being more preferred.

The extruder 25 is conventional, e.g., a standard 3 /2 inch extruder.The die 22 is an unconventional circular cross head die which is somachined as to provide a 3% inch opening for the slightly inflatedtubing 10. The details of the die 22 may be better appreciated byreferring to FIGS. 2 and 3. The opening 26 through which the inflatedsubstrate passes has been cut through mandrel 27 which is attached tothe die housing 28. The path of the molten coating material 23 isindicated by the arrows in FIGS. 2 and 3.

The vacuum chamber 21 puts a mild vacuum, e.g., in the range from 0 toabout 3 inches of water, on the die 22 to draw or suck in the extrudedcoating 23 while it is still molten against the inflated tubing 10 toprevent the formation of occluded bubbles in the laminate 24. The vacuumchamber 21 can simply consist of a cylindrical housing whose innerdiameter closely conforms to the outer diameter of the inflated tubing.The vacuum can be applied through outlet 29 by a conventional vacuumhose.

The molten ethylene vinyl acetate copolymer coating 23 is extrudeddirectly onto the predominantly polyethylene tubing with the temperatureof the die 22 being typically about 420 F., and then cooled by the waterspray from cooling ring 30. Pinch rollers 31 collapse the now formedlaminate 24.

The process is repeated as the two-ply laminate 24 is inflated andpassed through die 32 where it becomes three-ply laminate 33 as coating34 is applied. Cooling ring 35, extruder 36 and vacuum chamber 37 servethe same function as before. The tube is also inflated slightly by abubble 40 trapped between pinch rollers 41 and 42 in the same manner asthe bubble 20 is trapped between pinch rollers 18 and 31.

The most preferred polymer mixture for this critical outer layer isillustrated in the graphs of FIGS. 7 and 8 in two graphicrepresentations. The preferred and desired outer lamina for achievingthe desired abuse characteristics as described in more detail under theheading Package Abuse Test in this application would be a mixed polymermaterial containing between 30- 58% by weight of isotacticpolypropylene, 22-50% by weight of polybutene-l and 5-20% by weight ofacetic polypropylene. For certain special applications mechanicalmixtures containing 30-72% by weight of isotactic polypropylene, 10-50%by weight of polybutene-l and O-20% by weight of atactic polypropylenemay be satisfactory and in other limited applications where abuse andquality standards are not very critical a mechanical mixture of therange of 0-72% by weight of isotactic polypropylene, 050% by weight ofpolybutene-l and 0-.

50% by weight of atactic polypropylene may be suitable. Of course,additives such as stabilizers and the like may be included as inconventional in the practice of this art.

In the preferred embodiment the wall thickness of the substrate tubingprior to orienting would be 15 to 25 mils with the most preferredthickness being about 20 mils.

The preferred thickness of the first coating is 1 to 3 mils with themost preferred thickness being about 2 mils. The preferred thickness ofthe second coating is 5 to 15 mils with the most preferred thicknessbeing about 10 mils. The thickness of the most preferred laminate 33prior to orienting would be about 32 mils. The laminate 33 as it passesthrough the pinch rollers 42 and over guide rollers 43 is thussubstantially unstretched and unoriented.

A hot water bath tank 44 containing water 45 at about 212 F. raises thetemperature of the laminate 33 to its orientation level. The laminate 33is continually heated in hot water bath 45 to a temperature at or belowthe melting point of the substrate and the outer coating and thenstretch oriented by the blown bubble technique. In the most preferredinstance the temperature of the bath is maintained at about 212 F. Somevariation is usually possible, however, and water temperatures of about205? F. are operable in proper circumstances.

After the temperature of the inner and outer lamina tubing is adjustedto the proper orientation level and the temperature of the inner laminais adjusted to above its orientation temperature the bubble 46 is-blownand the fihn is stretched in both the transverse and longitudinaldirections must preferably in a ratio of about 3.611 longitudinally and4:1 transversely, thus reducing the thickness of the laminate 33 toabout 2.5 mils thickness. The coatings and the substrate are reducedequally. Blow ratios of 3.4 to 4:1 in the longitudinal direction and 3.5to 4.521 in the transverse directionvare generally satisfactory and incertain instances blow ratios of 3.0 to 45:1 in the longitudinaldirection and.3.0 to 4.5 :1 in the transverse direction may be used.Biaxially stretching should preferably be about 14.5 :1 and in certaininstances may vary from 9:1 to 20:1. It is an important feature of thisinvention that the laminate be orientable out of hot water to produce alaminate with the desired physical characteristics, particularlyshrinkability in hot water, at a reasonable cost. The bubble 46 isfinally collapsed by rollers 47 and the laminate is conveyed throughpinch rollers 48 and rolled onto windup roll 49.

When the ethylene vinyl acetate copolymer with about 9 /2 vinyl acetateis raised to a temperature of 212. F., it is slightly above itscrystalline melting point-The crys.

.5 talline melt point is approximately 209 F. For proper performance themelt point of the intermediate ply should preferably be below 212 F. inthe usual ciricumstance. The blowing causes the melted ethylene vinylacetate copolymer layer to flow and become hot blown and thus"substantially unoriented while the irradiated or crosslinkedpolyethylene layer becomes highly oriented as does the outer layer ofpolymer. The resistance to tearing exhibited by the laminate is due inpart to the fact that the copolymer was melted at the usual orientationconditions of the irradiated polyethylene and the outer lamina andbecame hot blown rather than oriented.

In FIG. 4 a cross-section of the laminate 33 is illustrated showingsubstrate 10, coating 23 and coating 34. FIG. 5 shows a cross-sectionthrough a bag 50 which can be made from the laminated tubing 33. Thetubing can be transversely cut and heat sealed resulting in a seal 51which closes off one end of the tubular segment. The other end is leftopen to receive a product such as a turkey, beef round, etc. It is thisopen end to which attention is now'drawn. The lips or edges 52 and 53 ofthe bag curl outwardly instead of lying flat as they would in the caseof a non-laminated thermoplastic bag. Since the outer layer of the bagis apparently stressed more than the coating andsubstrate layers, thereis an outward curl. The outward curl of the bag lips has the advantageof making the bags easier to open. On production lines where bags areopened manually and the product inserted therein even a short delayencountered in opening a bag is costly; Bags made from non-laminatedfilm have lips which lie flat and tend to adhere to each other. Thecurled lipon the bags made from film according to the present inventionenables a worker to more easily separate the bag lips and open the bag,thus increasing production. FIG. 6 further illustrates a bag or pouchmade from the tubular laminate.

Heat seals, such as heat seal 51 in FIG. 5, are improved because of thelower irradiation dosage given the substrate which normally will serveas the sealing surface in a packaging application of the presentinvention. It will also be understood that die 22 and die 32 may bealigned and the tubing may be passed sequentially through the respectivedies without the necessity for intermediate cooling and collapsing ofthe tubing as shown at 30 and 31. A single two ply coating die couldalso be used. It would also be possibleto carry out the procedure inentirely separated stages by winding the collapsed film up after eachprocedure. In this manner the procedures could be carried out atdifferent locations or in a particular plant situation that did notallow for the proper juxtapositioning of the equipment for thecontinuous procedure shown in FIG. 1.

{The invention is best illustrated by the following examples.

I 7 EXAMPLE I Following the procedure as schematically outlined inFIGJl, a'n' ethylene vinyl acetate copolymer containing 3 /2% vinylacetate (DuPont Alathon 3445) is feed into the extruder hopper ofextruder 9 which is a 3% inch Harting Extruder and "is operated at thefollowing temperatures: rear zone 325 F., mid-barrel 375 F., frontbarrel-400 F.-, adaptor 300 F.;"and die 360 F. The screw r.p.m. :is 13and the pressure is 3,300 p.s.i. The die diameter is 3.5 inches and. thetubing circumference pro- ."duced' is 8- inch. The water from thecooling ring 12 is 4244). The resin is fed into the hopper of extruder25 which is a 1% inch Prodex Extruder operated with a cross head die ofthe type illustrated in FIGS. 2 and 3. The second extruder is operatedat the following temperatures: rear zone 325 F., midbarrel 375 F., frontbarrel 400 F., adaptor 300 F., and die 360 F. The screw rpm. is 13 andthe pressure is 3,300 p.s.i. The die diameter is 3.5 inches and thetubing circumference is 8 inches. The top rolls 18 are operated at 14.0feet per minute and the bottom rolls 31 at 14.5 feet per minute. Thewater from the cooling ring 30 is at 62 F. and the coating thickness isapproximately 2 mils.

The second coating resin is a mixture of 53.3% by weight of isotacticpolypropylene (Novamont 1 F007), 33.3% polybutene-l (Mobil PB 103) and13.3% atactic polypropylene (Novamont 1 Lot 2030). The atactic andisotactic polypropylene are first added in proper proportion to aBanbury mixer and melt blended for approximately 8 minutes at 400 F. andthen extruded into a sheet which is diced into pellets. These pelletsare combined with pellets of polybutene-l in a rotating drum and thisadmixture is charged to the hopper of the second coating extruder whichis depicted at 36. The extruder 36 is a 2 /2 inch N.R.M. Extruder and itis operated at the following temperatures: rear zone 385 F., mid-zone400 F., forward zone 450 F., adaptor 400 F. and die 425 F. The screwrpm. is 32. The top rolls 41 are operated at 14.5 feet per minute andthe bottom rolls 42 at 15.0 feet per minute. The water from the chilledring 35 is at 62 F. and the coating thickness is approximately 10 mils.

Biaxial orientation is carried out by pre-heating in water 210 F. to 212F. as shown at 44 of FIG. 1 and passing the thus heated tubing throughpinch rolls operating at 15 feet per minute to deflate rolls operatingat 56 feet per minute and blowing the 4 inch wide tubing to produce afilm width of approximately 16 inches with a film thickness ofapproximately 2.5 mils. This tubing is then rolled up on a storage rollwhich is delivered to a converter who prepares the bags by sealing thebottoms of the bags in a conventional manner and obviously severing thetubing in the desired bag lengths.

Examples IIXVI The above procedure was repeated except for the variationin the outer coatings composition as illustrated in the graph of FIG. 7with plots 2-16. Of course, in Example 6, 7 and 14 no polybutene-lmixing procedure was carried out and in Examples 10, 16, 15, 11 and 8,no atactic polypropylene-isotactic polypropylene combining or mixingprocedure was carried out and in Example 9 no mixing procedure wascarried out.

PACKAGE ABUSE TESTS The following tests were run under commercialconditions using bags made from tubing made substantially as describedin Example I. The tests were made in a commercial plant and involved thepackaging of dressed turkeys having weights of approximately 20 to 22pounds in bags made according to this invention that were 16.5 incheswide and 24 inches deep and regular commercial polyethylene bags soldunder the L-film Trademark of W. R. Grace & Cos Cryovac Division, theassigneee of the present application, which were produced from tubingmanufactured in a manner generally corresponding to that taught in Pat.3,022,543 which was mentioned earlier in this application. These bagswere 16.0-16.25 inches wide and 23 inches deep.

The birds were inserted into marked intermixed bags of the two types onthe packaging line in; conventional 1 Novamout is'a. trademark 'of theNovamont Corp. Mobil is a. trademark of the Mobil Oil Co.-.

manner and the loaded bags were vacuumized on a lift New shippingcartons were used in the abuse tests in nozzle and the bag necks twistedand clipped as is usual. two sizes, large box 22- /2" x 16 x 9" andsmall box The closed bags were passed through hot water shrink 21 /2" x15" x 9". Two removable box bottoms, made tunnels in conventional manneroperated at between 205- of pressed Wood, were made to exactly fit thebottoms 208 F. and shrunk also in conventional manner. The tunof therespective boxes. Two pieces of pressed wood of nels were run at 36 feetper minute. 5 the same size as the box bottom flaps were glued to eachThe following charts show the results noted through of the pressed woodbottoms. These wooden bottoms were the tunnel. placed in the boxesduring the test to simulate the actual PACKAGING BREAKAGE rEmonmgr o i znnnsoN FOR REJECT OR LOCATION OF URE Clip Neck Elbow Wing Air in SealsHock out puncture puncture tip bags 1 Unlmown I New bags 1 6 2 3 6 91 1Standard bags 4 26 32 8 5 9 81 14 1 hAir in bigs means bags came out oftunnel ballooned and reason could not be determined at product on nospee s.

1 Unknown means bags were torn to such an extent that origin of tearcould not be determined.

Total loss on New Bags-120 out of 2,000=6%. box bottoms which would havethe two bottoms flaps Total 1055 on Standard Bags-479 out Of exposed onthe inside of the box. The edges of these After h g Operation the Secondl y it Was deterfiaps are a major cause of damage to packages shippedmined that Q 1n the s Was h e 111 most cases by in such boxes. Thistechnique helped to make sure that Operator 105mg vacuum 111 the PP P Ifthe each time the tests were repeated on the shaker machine,

rejects (111i 110 the a in the bags are subtracted from the abrasiveforce of the box bottoms would be the same. the total breakage the datawould show New Bags The frozm turkeys were rebagged w per b one29/2O0=1-45%: Standard Bags 98/200=4'90%' in the new bag of thisinvention, which was 16" x 24" FROZEN PACKAGE ABUSE and had a gauge of2.4 to 2.8 mils. The other was pack- PERFORMANCE 30 aged in a Perflex 3S 2.3 to 2.7 mils 16" x 24-' polyethylene bags. I

The a check e on the e The bags on the frozen turkeys were shrunk in ahot out of the test birds from a standard liquid freezer which water diptank at F. boxed in the test boxes with included considerable bumping ofthe frozen packages the false bottoms of pressed wood, and put on theshaker tes and conve ors. The total numgzg fg rgi 2 32523 due totheypackofi procedure machine set at 250 r.p.m. Prehminary tests showedthat o own h ckif fig gf if f fgfgg fi m vmg d t 6 pa 0 the New Bags andthe Perflex S bags. By guess, it was The following procedure was used:100 New Bags and found that a test time of 10 minutes later reduced to 8min- 100 Standard Bags were randomly checked. They could 40 would notdestroy the bags on the turkeysbe identified by an A seal marke o th N BEach turkey was examined for-possible bag breakage and an S seal markeron the Standard Bags. This was on the two wing elbows, back, and hockfor a possible repeated five times. total breakage of 4 breaks per bird.Data 18 recorded 111 3rd 5th Percent 1st 100 2nd 100 100 4th 100 100Total breakage b 13---- 1 r 12 9 12 so 12 ijg rida i l bagsflz 26 (6rejects)- 28 (8 rejects). 23 21 (5 rejects)- 22 120 24 The number in thele is the number of bags P the Table. Then the turkeys were rebaggedreversing alhundred that had holes in them- 'h f punctures had ternatelythe new turkey bags and Perflex 8 bags on each occurred since beingplaced in the liquid freezer under bird with each turkey being used 3 4times in the-tes}.

normal packing house operating procedures. The turkeys Were used in thistest not more than twice Q Y centfol used the fouewmg Prmedqm: If in anyone day in order to insure thatthey were solidly there IS a puncture mthe bag (lookmg from the breast frozen while being tested. The birdswere refrozen'and side), it is rejected or returned for rebagging; ifthe tear d o ht in the freezer. or puncture is on the back side, it isnot re ected unless Store vermg the puncture is longer than /2 inch.conci'on There were 60 New Bags with punctures and no re ec ts a v in500 random samples. There were 120 bag punctures in Data presented inthe Table She-W5 box Size is kssifib the Standard Bags with 19 rejectsin a random sample 6 portant than the kind of turkey bag as a cause ofbreakage. of O l i 5 Turkeys in the new turkey bags were significantlymore 1 one as on resistant to abuse generated in the shaker test thanPerflex The Ne Bag h s definite advantages in the P S turkey bags. Ofthe potential breaks, 26.78% occurred duction line, but the most notedadvantage is in the freezin the new bags, or one i f hil i h P fl S ingand pack-out operation where breakage is only about bags 47 02% orroughly two in four occurred This g 1/2 of Standard Bagsference isstatistically significant at as high as0.995.-In

SIMULATED SHIPPING TEST other words, there is hardly any doubt that thelower Twenty-four Grade A 18 lb. 1 oz. to 19 lb. 15 02., mean failurerate of the new s p e i bagged and frozen torn turkeys were purchasedfrom a chain grocery store. 5 a Trademark of Union Carbide.

a test time of 30 minutes on the shaker destroyed both COMPARATIVE ABUSERESISTANCE OF NEW BAGS AND PERFLEX S BAGS ON FROZEN TURKEYS Percentpoten- Shipping Total Total tie Bags usedcartons Number of breaks perbird in bags on frozen turkeys 1 breaks packages breakl New bags Smallbox-.. 2 1 0 2 2 1 1 1 1 1 1 3 1 2 0 1 2 2 0 0 24 84 28.57 Large box..-2 2 1 1 1 2 1 1 0 1 0 1 2 0 1 3 1 0 0 0 1 21 84 25.00

Total 4 2 2 1 3 4 2 2 1 2 1 2 5 1 3 3 2 2 2 0 1 45 168 26. 78

Perflex S bags Small box... 1 1 3 1 3 0 3 1 2 0 2 4 2 3 1 2 3 1 1 2 1 3784 44. 04 Large box... 3 2 4 2 3 1 2 3 1 0 0 4 2 2 3 2 1 2 3 1 1 42 8450. 00

Total 4 3 7 3 6 1 5 4 3 0 2 8 4 5 4 4 4 3 4 3 2 79 168 47.02

1 Each turkey checked for resistance to abuse could be broken at the 2elbows, back and hook for a total of four breaks per turkey.

In the Graph of FIG. 7

D=Unprocessable Region E=Borderline Processability F=Area of Poor GlossG=Area of High Tack and Poor High Temperature Strength I-I==Area ofModerate Tack and Rapidly Decreasing High Temperature StrengthI=Preferable Area I claim:

1. A heat shrinkable, oriented laminated plastic film comprising:

(a) a tubular cross-linked thermoplastic film substrate and (b) an outerlayer comprised of a mixed blend of polymers in the ratios by weightselected from the group consisting of 30%72% isotactic polypropylene,10%-50% polybutene-l and 5%20% atactic polypropylene.

2. The plastic film of claim 1 wherein (b) is a mixed blend of polymersin the ratios by weight set forth selected from the group consisting of3058% isotactic polypropylene, 22-50% polybutene-l and 5-20% atacticpolypropylene.

3. The plastic film of claim 2 wherein (a) is a predominantlypolyethylene film, an intermediate lamina of a copolymer of ethylenevinyl acetate having 7-13 vinyl acetate is interposed between laminas(a) and (b) and secures said lamina together.

4. The plastic film of claim 3 wherein laminas (a) and (b) aresubstantially oriented and the intermediate lamina is substantiallyunoriented and said laminate is heat shrinkable, wherein lamina (a) issubstantially twice as thick as lamina (b) and the intermediate laminais substantially /s as thick as lamina (b) and said laminate is between2 and 3 mils thick and wherein the orientation temperature of lamina (a)and lamina (b) is below 212 F. and the melt temperature of theintermediate lamina is below 212 F. whereby said laminate has beenstretch oriented in hot water by the trapped bubble technique.

References Cited UNITED STATES PATENTS 2,855,517 10/1958 Rainer et al204-159.2 X 3,486,196 12/1969 Klenk et al. 264-173 X 3,508,944 4/1970Henderson et al. 264173 X 3,022,254 2/1962 Baird, Jr. et al. 1l773,274,004 9/1966 Curler et a1 16l256 X 3,595,735 7/1971 Tyrrell 16l256 XGEORGE F. LESMES, Primary Examiner P. C. IVES, Assistant ExaminerU.S.Cl.X.R.

